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What causes a graben to form?
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tectonic basins and rift valleys
Escarpments of the Great Rift Valley rising above the plain north of Samburu Game Preserve, central Kenya. Beisa oryxes graze in the foreground.
A graben is a depressed block of the Earth's crust that forms primarily due to the extension of the crust. As tectonic plates or large crustal blocks diverge, the brittle crust fractures, creating a gap into which a central block of rock slides downward.12
This process is characterized by the following geological mechanics:
- Faulting: The block is bounded on at least two sides by steeply dipping normal faults that dip toward each other.13
- Tensional Forces: The formation is driven by lateral tension, which may be caused by regional uplift or the formation of features like salt domes.1
- Resulting Landforms: As the central block drops, it creates a tectonic depression or "ditch," often forming a rift valley with a relatively flat floor and steep, mountainous sides.12
While grabens are most commonly associated with crustal extension, they are distinct from compressional features like ramp valleys or foreland basins, which result from crustal shortening. Famous examples of graben-formed landscapes include the Jordan–Dead Sea depression and Death Valley.21